I have conflicting notes thats say:

While NumRef >= 0 ;<--- Because the number of refs is always 1 higher than the list of refs that start at 0.
Target = MyCell.GetNthRef(NumRef, 0x3E) as actor
NumRef -= 1

However...

While NumRef > 0 ;<--- I am seeing this in other people's scripts and on the wiki
Target = MyCell.GetNthRef(NumRef, 0x3E) as actor
NumRef -= 1

Which is correct?

I suspect you're seeing the decrement first in those. i.e.

While NumRef ;(which implies > 0)
NumRef -= 1
Target = MyCell.GetNthRef(NumRef, 0x3E) as actor

Since 0 is a valid value, you want to include it. In your first example, won't it fail the first time, because the index is too high?